WO2015003779A2

WO2015003779A2 - Device and method for modelling a cornea

Info

Publication number: WO2015003779A2
Application number: PCT/EP2014/001791
Authority: WO
Inventors: Harald P. STUDER; Hansjörg Riedwyl; Philippe Büchler; Cynthia J. ROBERT
Original assignee: Iss Integrated Scientific Services Ag
Priority date: 2013-07-10
Filing date: 2014-06-30
Publication date: 2015-01-15
Also published as: EP2824599A1; ES2665146T3; WO2015003779A3; US10181007B2; EP3019990B1; US20160162630A1; EP3019990A2

Abstract

In order to model a cornea for simulating tissue sections in the cornea a patient-specific finite element model of the cornea is generated (S2). A first group of tissue sections with main fibres running parallel to the cornea surface are distributed in the finite element model according to a first distribution function (S22). A second group of tissue sections with inclined crosslink fibres running non-parallel to the cornea surface is produced in the finite element model according to a second distribution function (S23). The second distribution function distributes (S23) the crosslink fibres with a non-uniform weighting function over the depth of the cornea, from the outer surface of the cornea to the inner surface thereof.

Description

DEVICE AND METHOD FOR MODELING A HORN SKIN

Technical area

The present invention relates to a device and a method for modeling a cornea. More particularly, the present invention relates to a computerized apparatus and method for modeling a cornea for simulating tissue sections in the cornea, the computerized apparatus comprising a processor programmed to generate a patient-specific corneal finite element model.

State of the art

Numerous vision defects such as myopia (myopia), hyperopia (farsightedness) or astigmatism (astigmatism) are today corrected with surgical procedures on the eye. The refractive correction of the eye takes place predominantly by means of ophthalmic laser systems which cut and / or ablate the eye tissue, in particular the cornea (cornea), in order to approximate the optical power of the eye as well as possible to a desired value. Although tissue sections can be performed extremely precisely by laser pulses, much more accurately than comparatively manually with a scalpel, the change in tissue shape resulting from tissue sections due to intraocular pressure still makes it very difficult to plan sections and predict cut results.

To improve the ophthalmological refractive correction, WO

02/07660, WO 94/1 8636, US 2009/31 8907 and US 2009/1 87386 the

Modeling the eye with finite element analysis. The finite element can do this

Model of the eye can be used for the simulation of tissue sections. WHERE 02/07660 describes the introduction of a layer model of the cornea, with several layers of different hardness. US 2009/318907 and US 2009/1 87386 describe a general axisymmetric model based on a non-linear elastic, easily compressible and transversally isotropic formulation. US 2009/1 87386 moreover describes a connection of the cornea to the sclera with a preprogramming of peripheral elements for imaging a firm connection of the cornea to the sclera (limbus), which does not occur in cuts that extend beyond the cornea into the adjacent sclera can be sufficient. Moreover, the known solutions provide no information as to how the stromal swelling pressure flows into the modeling.

In recent years, the inhomogeneity of the cornea has been thoroughly studied over its depth, especially in:

Quantock AJ, Boats C, Yount RD, Hayes S, Tanioka H, Kawasaki S, Ohta N, Lida T, Yagi N, Kinoshita S, Meek KM, (2007); "Small-angle fiber diffusion studies of corneal matrix structure: a depth-profiled investigation of the human eye-bank cornea"; Journal of Applied Crystallography, 40: 335-340;

Palka BP, Tanioka H, Sotozono C, Yagi N, Boats C, Young RD, Meek KM, Quantock AJ, (2008); "Reduced collagen interfibrillar spacing in macular corneal dystrophy occurs predominantly in deep stromal layers"; Investigative Ophthalmology & Visual Science, 49: E-Abstract 3926;

Kamma-Lorger CS, Boats C, Young RD, Hayes S, Quantock AJ, Meek KM, (2008); "Depth profile study of molecular collagen structure in normal human cornea; Acta ophthalmologica", 86: 243; Meek KM, Boats C, (2009); "The use of X-ray scattering techniques to quantify the orientation and distribution of collagen in the corneal stroma"; Progress in Retinal and Eye Research, 28: 369-392;

Kamma-Lorger CS, boats C, Hayes S, Moger J, Burghammer M, Knupp C, Quantock AJ, Sorensen T, Di Cola E, White N, Young RD, Meek KM, (201 0); "Collagen and mature elastic fiber organization as a function of depth in the human cornea and limbus"; Journal of Structural Biology, 1 69: 424-430; and

Petsche SJ, Chernayak D, Martiz J, Levenston ME, Pinsky PM, (201 2); "Depth-Dependent Transverse Shear Properties of the Human Corneal Stroma"; Investigative Ophthalmology & Visual Science, 53 (2): 873-80.

It was discovered that the tissue is becoming weaker and weaker across its depth, ie from the front / outside (anterior) to the posterior / posterior, and in particular the shear stiffness is significantly reduced. The reason was found in the fact that in the anterior / outer layers there are many inclined collagen fibers that do not run parallel to the corneal surface. Inclined fibers, or so-called cross-link fibers, give the fabric shear stiffness. Opposite are the neatly stacked fibers running parallel to the surface in the deep (back / inner) layers.

Various mathematical material definitions for simulating the biomechanical properties of the corneal tissue have been developed and published in the last decade, in particular in:

Bryant M, McDonnell P, (1 996); "Constitutive laws for biomechanical modeling of refractive surgery". Journal of Biomechanical Engineering, 1 1 8 (4): 473-481; Pinsky PM, Van der Heide D, Chernyak D, (2005); "Computational modeling of mechanical anisotropy in the cornea and sclera"; Journal of Cataract and Refractive Surgery, 31 (1): 1 36-145;

Alastrue V, Calvo B, Pena E, Doblare M, (2006); Biomechanical Modeling of Refractive Surgery, Journal of Biomechanical Engineering, 1 28: 1 50;

Lanchares E, Calvo B, Cristobal J, Doblare M, (2008); "Finite element simulation of arcuates for astigmatism correction"; Journal of Biomechanics, 41: 797-805;

Pandolfi A, Manganiello F, (2006); "A model for the human cornea: constitutive formulation and numerical analysis"; Biomechanics and Modeling in Mechanobiology, 5 (4): 237-246;

Pandolfi A, Holzapfel G, (2008); "Three-dimensional modeling and computational analysis of the human cornea considering distributed collagen fibril orientations"; Journal of Biomechanical Engineering, 1 30 (6); and

Pandolfi A, Fotia G, Manganiello F, (2009); "Finite element simulation of laser refractive corneal surgery"; Engineering with Computers, 25: 1 5-24.

The creation of a patient-specific finite element model of the cornea was described in Studer HP, Riedwyl H, Amstutz CA, Hanson VM, Büchler P, (201 3); Patient-specific finite-element Simulation of the human cornea: A clinical validation study on cataract surgery; Journal of Biomechanics, 46 (4): 751-758. The effect of cataract incisions was numerically simulated for patients. Studer et al. However, in this document, it is explicitly stated that neither material parameters nor the distribution of collagen fibers were patient-specific, and that too Depth dependence of mechanical properties within the corneal thickness was neglected. They also concluded that considering the individual corneal topography of a patient is more relevant for accurate prediction of the postoperative corneal shape than precise determination of patient-specific material properties.

Mathematical material definitions for simulating the biomechanical properties of the corneal tissue, in which the inclinated fibers are taken into account, can only be found in the following documents:

Studer HP, Larrea X, Riedwyl H, Büchler P, (201 0); "Biomechanical model of human cornea based on stromal microstructure"; Journal of Biomechanics, 43: 836-842; and

Petsche SJ, Pinsky PM, (201 3); "The role of 3-D collagen organization in stromal elasticity: a model based on X-ray diffraction data and second harmonic-generated images"; Biomechanics and Modeling in Mechanobiology.

In the latter document, Petsche SJ, Pinsky PM, defines a three-dimensional distribution function (all directions in the spherical coordinate system), which simultaneously models the weighting of the main as well as the inclinated fibers. Using this weighting, the authors describe the amount of collagen fibers that run in a certain direction. The fibers themselves are described as material anisotropy in the continuum.

Presentation of the invention

It is an object of the present invention to propose an apparatus and method for modeling a cornea that enables the simulation of tissue sections in the cornea. It is in particular a task of The present invention proposes a device and a method for modeling a cornea which do not have at least some disadvantages of the known systems.

According to the present invention, these objects are achieved by the features of the independent claims. Further advantageous embodiments are also evident from the dependent claims and the description.

A computerized apparatus for modeling a cornea for simulating tissue sections in the cornea includes a processor programmed to load patient-specific corneal data, to generate a patient-specific corneal finite element model, and in the finite element model, based on cutting data defining the tissue sections To determine elements that are separated by the tissue sections.

The above-mentioned objects are achieved by the present invention in particular in that the processor of the computerized device is further programmed to distribute a first group of tissue fibers, with main fibers running parallel to the outer surface of the cornea, according to a first distribution function in the finite element model, and distributing a second group of tissue fibers, with inclined, non-parallel to the outer surface of the cornea extending cross-link fibers according to a second distribution function in the finite element model, the second distribution function, the crosslink fibers with a non-uniform, decreasing depth distribution function over the Depth of the cornea, from the outer surface of the cornea to the inner surface of the cornea, distributed. In one embodiment, the processor is programmed to distribute the cross-link fibers over the depth of the cornea with a sinusoidal depth distribution function. The depth distribution function has a sinusoidal course, at least in a defined partial area (eg in one third) of the thickness or depth of the cornea, which is limited to a section of the sinusoid, which decreases the depth distribution of the crosslink fibers from the outer surface of the cornea defined inside surface of the cornea.

In one embodiment, the processor is programmed to introduce in the finite element model permeability values for fluid exchange in the corneal tissue, which depend on the depth of the cornea.

In one embodiment, the processor is programmed to introduce in the finite element model permeability values for fluid exchange in the corneal tissue, which depend on the depth distribution function with which the crosslink fibers are distributed over the depth of the cornea.

In one embodiment, the processor is programmed to create a transition from the patient-specific finite element model of the cornea to a population-based sclera model, and to distribute the cross-link fibers in transition with a decreasing depth distribution function across the depth of the transition, from an outer transition surface that extends from the outer surface of the cornea to the outer surface of the sclera, to an inner transitional surface extending from the inner surface of the cornea to the inner surface of the sclera. In one embodiment, the processor is programmed to distribute the cross-link fibers in the finite element model to a plurality of layers parallel to the outer surface of the cornea, and to distribute the crosslink fibers in the layers, each with a two-dimensional distribution function.

In one embodiment, the processor is programmed to store in the finite element model different material properties for the first group of tissue fibers and the second group of tissue fibers.

In one embodiment variant, the processor is programmed to distribute the main fibers in the finite element model evenly over a plurality of surfaces or layers running parallel to the outer surface of the cornea and to distribute them on the surfaces respectively in the layers, each with a two-dimensional distribution function.

In addition to the computerized apparatus for modeling a cornea, the present invention further relates to a computer-implemented method for modeling a cornea for the simulation of tissue sections in the cornea, and a computer program product comprising a non-transient computer-readable medium with computer program code stored thereon, which is arranged to control a processor so that the processor executes the procedure for modeling the cornea. The computer-implemented method comprises the processor performing the following steps: loading patient-specific corneal data, generating a patient-specific corneal finite element model; Distributing in the finite element model of a first group of tissue fibers, with main fibers running parallel to the outer surface of the cornea, according to a first distribution function; and distributing in the finite element model a second group of tissue fibers, with incised, not parallel to the outer surface of the Corneal cross-link fibers, according to a second distribution function, wherein the second distribution function distributes the cross-link fibers with a non-uniform depth distribution function across the depth of the cornea, from the outer surface of the cornea to the inner surface of the cornea, and determining, on the basis of Tissue sections defining cutting data, of elements in the finite element model, which are separated by the tissue sections.

Brief description of the drawings

Hereinafter, an embodiment of the present invention will be described by way of example. The example of the embodiment is illustrated by the following attached figures:

Figure 1: shows a block diagram of a computerized device for

Modeling a cornea for the simulation of tissue sections in the cornea.

FIG. 2: shows a flow chart with an exemplary sequence of steps

Method for modeling a cornea for the simulation of tissue sections in the cornea.

FIG. 3: shows a flow chart with an exemplary sequence of steps for

Loading eye data.

FIG. 4: shows a flowchart with an exemplary sequence of steps for

Creation of a finite element model of a cornea for the simulation of tissue sections in the cornea. Figure 5 shows schematically in cross section of a corneal segment, the distribution of parallel to the surface of the cornea extending main fibers over the depth of the cornea (depth distribution) and a corresponding distribution or depth distribution function or weighting function.

FIG. 6 shows schematically in cross-section of a corneal segment the distribution of inclined, not parallel to the surface of the cornea extending cross-link fibers over the depth of the cornea (depth distribution) and a corresponding distribution or depth distribution function or weighting function.

FIG. 7 shows schematically in cross-section a transition of a corneal segment to an adjacent sclera segment and the distribution of inclined, not parallel to the surface of the cornea extending cross-link fibers across the depth of the cornea and the transition.

FIG. 8 shows a two-dimensional distribution function for main fibers running parallel to the surface of the cornea and inclined, not parallel to the surface of the cornea extending cross-link fibers.

Ways to carry out the invention

In Fig. 1, reference numeral 1 refers to a computerized apparatus for modeling a cornea for the simulation of tissue sections in the cornea. The device 1 comprises an operable computer with at least one processor 1 0 and a memory 1 1 connected to the processor 1 0 for storing data (data memory) and computer program code (program memory). In the embodiment according to FIG. 1, the device 1 comprises Moreover, a display 1 2, for example, an LED or LCD screen. As shown schematically in FIG. 1, the device 1 is connected in a variant to a computerized data source 2 external to the device 1, for example via a wired or wireless communication interface. The data source 2 comprises one or more processors and is arranged to transmit eye data, including patient-specific corneal data and / or population-based scleradata, to the device 1, as will be described in more detail later. Depending on the embodiment variant, the data source 2 comprises an ophthalmological measuring device for detecting the patient-specific corneal data from a patient and / or an ophthalmological database with population-based scleradata.

The processor 10 is configured or programmed to perform a method of modeling a cornea for simulating tissue sections in the cornea. The apparatus 1 comprises for this purpose a computer program product with a computer-readable medium, which is permanently or removably connected to the processor 10 and includes computer program code stored thereon, which is set up to control the processor 10 to execute the method. In the following sections, possible sequences of steps for carrying out the method will be described with reference to FIGS. 2, 3 and 4.

As shown in FIG. 2, eye data is loaded into the memory 11 in step S1.

As can be seen in FIG. 3, in the optional step S1 1, population-based scleradata are loaded into the memory 11. The population-based scleradata define a geometric average sclera model including three-dimensional geometry and dimensions of an average sclera, on a statistical scale Database. In one embodiment, the sclera data defines at least the geometry and dimensions of a border region of the sclera adjacent to the transition to the cornea. The sclera data are obtained, for example, from an internet-based data source or are permanently stored in the data memory 11.

In step S1 2, patient-specific corneal data are loaded into the memory 11. The patient-specific corneal data define a patient-specific model of the cornea including three-dimensional geometry and dimensions of the cornea of a patient on a metrologically recorded database. The patient-specific corneal data are preferably recorded by means of an ophthalmological measuring device and stored in the data memory 11 associated with the relevant patient.

As shown schematically in FIG. 2, the processor 10 generates in step S2 an initial finite element model based on the charged eye data, in particular a patient-specific finite element model of the cornea based on the patient-specific corneal data.

In one embodiment, a spherical finite element mesh is initially generated which is transformed into the patient-specific (defined by the patient-specific corneal data) geometry of the cornea 34 by means of a transformation method, for example a transformation method as described in Studer HP, Riedwyl H, Amstutz CA, Hanson VM, Büchler P, (201 3); Patient-specific finite element Simulation of the human cornea: A clinical validation study on cataract surgery; Journal of Biomechanics, 46 (4): 751-758. As can be seen in FIG. 4, in the optional step S21 the processor 10 generates a transition from the patient-specific cornea to the population-based sclera. This is advantageous because a part of the sclera is also simulated for a precise simulation of surgical interventions. As illustrated in FIG. 7, a smooth geometric transition 36 is created from the patient-specific cornea 34 to the population-based sclera 35. In particular, for the transition 36 from the patient-specific cornea 34 to the population-based sclera 35 mathematical functions for geometric surfaces are defined, a function

for the front / outer transition surface (anterior) and a function

for the posterior / internal transition surface (posterior). The front / outer transition surface

is formed as a smooth surface and extends continuously from the front / outer surface 30 of the cornea 34 to the front / outer surface 350 of the sclera 35. The rear / inner transition surface

is formed as a smooth surface and extends continuously from the posterior / inner surface 33 of the cornea 34 to the posterior / inner surface 351 of the sclera 35. Depending on the embodiment, the transition 36 is generated on the basis of the patient - specific geometry model loaded in step S1 Cornea 34 or based on the corresponding finite element model of the cornea 34.

In step S22, the processor 10 distributes the main fibers 31 running parallel to the surface 30 of the cornea in the patient-specific finite element model of the cornea 34, as shown in FIG. 5. If necessary, the main fibers 31 are also transferred from the patient-specific cornea 34 in the transition 36 Population-based sclera 35 distributed.

The main fibers 31 are distributed on layers or surfaces of the cornea 34, each extending at different depths, parallel to the corneal surface 30. there For example, a two-dimensional distribution function is used (see example in Figure 8) to distribute the major fibers 31 within each of these corneal layers (in-plane). This two-dimensional distribution function consists of two parts:

which are combined as follows:

The weighting

between the two parts depends on the location of a material point

on the corneal layer and is given by:

where the distance of the material point to the corneal center (0,0), is the

Angle between the positive x-axis in the model and the connection between the material point and the corneal center, and Θ defines the fiber direction in the

local coordinate system of the material point

For the distribution (weighting) of the main fibers 31 to the individual corneal layers, a first depth distribution function is used. in the

Example of FIG. 5, the first depth distribution function is uniform (constant),

that is, the main fibers 31 are uniform across the depth

from the anterior corneal surface 30 to the posterior corneal surface 33, and has at each corneal depth (in each corneal layer) the same number of major fibers 31:

Thus, the main fibers 31 are distributed independently of the depth, parallel to the surface 30 as illustrated in FIG. 8, according to Equations (1) to (3). The skilled person will understand that due to other anatomical conditions, another depth distribution function for the main fibers 31 can be used.

Since parts of the transition 36 from the cornea to the sclera 35 are corneal tissue, the fiber distribution is also made in the transition 36. The main fibers 31 are also distributed in the transition 36 from the patient-specific cornea 34 to the population-based sclera 35 in the same way as in the cornea 34, within the parallel layers (areas) by means of the two-dimensional distribution function

and over the depth s according to the uniform first depth distribution function (weighting function) The homogeneous

Depth distribution of the main fibers 31 is shown schematically in FIGS. 5 and 7 so that the main fibers 31 are shown as layers or surfaces extending parallel to the corneal surface 30.

In step S23, the processor 110 distributes the inclinated cross-link fibers 32 in the patient-specific finite element model of the cornea 34, as shown in FIG. 6, not parallel to the surface 30 of the cornea. Optionally, the cross-link fibers 32 also become in transition 36 distributed from the patient-specific cornea 34 to the population-based sclera 35.

The cross-link fibers 32 are thus one of the main fibers 31 different fiber family, which are inclined by about 1 5 ° (the inclination is to be understood as a deviation from the direction of the main fibers), alternately "inward", ie the surface 33 inclined , and "outwards", so the surface 30 inclined. In a Variant are assigned to the main fibers 31 and the cross-link fibers 32 different material properties.

The cross-link fibers 32 become like the main fibers 31 by means of the two-dimensional distribution function described above

according to the equations (1) to (3), distributed within the corneal layers or surfaces (in-plane) running parallel to the corneal surface 30.

For the distribution (weighting) of the cross-link fibers 32 to the individual corneal layers, a second depth distribution function is used. in the

Example of Figure 6, the second depth distribution function (weighting function) on a decreasing with the depth s course. That means the cross-link fibers

32 are distributed as the number decreases across the depth s, from the anterior corneal surface 30 to the posterior corneal surface 33. In contrast to the depth distribution of the main fibers 31, the cross-link fibers 32 are thus not distributed uniformly (that is, not constant), but with a specific depth distribution function or weighting function over the depth s. In the example of FIG. 6, the second depth distribution function (at least in a defined subregion of FIG

Thickness or depth s of the cornea 34) has a sinusoidal course and is defined as follows:

In contrast to the uniform depth distribution of the main fibers 31 take

the cross-link fibers 32 with the depth s in the cornea 34 continuously. The skilled person will understand that due to other anatomical conditions as well another depth distribution function decreasing over the depth s for the

Crosslink fibers 32 can be used.

Since parts of the transition 36 from the cornea to the sclera 35 are corneal tissue, the fiber distribution and consideration of the depth inhomogeneity is also made in the transition 36. The cross-link fibers 32 are also distributed in the transition 36 from the patient-specific cornea 34 to the population-based sclera 35 in the same manner as in the cornea 34. Within the parallel to through the function

defined front / outer surface of the transition 36 extending layers, the cross-link fibers 32 by means of the two-dimensional distribution function described above

(in-plane), according to the equations (1) to (3) distributed. The inhomogeneous depth distribution is derived from the depth distribution according to equation (5). It applies

and thus

The inhomogeneous depth distribution of the cross-link fibers 32 is shown schematically in FIGS. 6 and 7 so that the cross-link fibers 32 are shown as inclined arrows whose length symbolizes their weighting (number, frequency).

Refractive surgical treatments, such as PhotoTherapeutic Keratectomy (PTK) and Laser Assisted Insitu Keratomileusis (LASIK), are known to result in peripheral corneal thickening. It is believed that the incisions of the treatment leads to relaxation in the tissue. This relaxation in turn leads to changes in the physiological imbibition pressure of the cornea, resulting in fluid shifts and swelling of the tissue. Fluid shifts through the tissue structure of the cornea can be considered as poroelastic problem and modeled using biphasic finite elements. In this case, both the linear and the non-linear case (in the latter, the material permeability - ie the permeability of the material for liquids - depends on the deformation) are mapped.

In step S24, the processor in the finite element model of the cornea 34 and optionally the transition to the sclera 35 introduces permeability values. The permeability values

characterize the fluid exchange in the corneal tissue and are determined depending on the depth s of the cornea 34. The permeability values

indicate the permeability of the corneal tissue for fluids depending on the depth s of the cornea 34. Since the depth distribution function for the incident fibers is directly related to the degree of collagen fiber adhesion and thus the impermeability of the tissue, the permeability dependent on the depth s may change

according to the following equation (7) depending on the depth distribution function of

Crosslink fibers 32 are modeled:

Thus, the change in permeability in the biphasic finite elements can be modeled via the depth s of the cornea and thus the depth-dependent swelling of the cornea.

The individual elements of the finite element model generated in step S2 with the initial geometry of the cornea 34 and the transition 36 to the sclera 35 each comprise a plurality of integration points with element values such as stress, strain, deformation, reaction force, plastic deformation, strain energy, etc. Here are these element values directional values calculated at the integration points from the parts contributed by the fibers. In an embodiment variant, different material properties for the main fibers 31 and the crosslink fibers 32 are provided and stored in the elements.

In step S3, the processor 10 carries out the solution calculation of the finite element model. In this case, the finite element model generated in step S2 is exposed to the initial geometry of the cornea 34 and the transition 36 to the sclera 35 (computationally) to the (for example, patient-specific measured) intraocular pressure. This leads to a (calculated) mechanical imbalance in the finite element model. As a result, the cornea represented in the finite element model is deformed (inflated) and the individual elements are deformed in the model. This results in a (calculated) strain in the elements of the model. Elongation is associated with a defined material function that determines how much stress is created due to a calculated strain. In fact, the fibers and distribution functions flow into this material function, which is calculated at each integration point. The material function relates stretch and energy (stress). The material function is defined by

the energy, the main fibers 31, the cross-link fibers 32 and the

Distribution functions are.

is a piece of fabric that is not made of fibers, and

is a penalty for volume changes (this leads to incompressibility of the tissue). The calculated voltage is then stored in the element again. This sequence of deformation -> strain -> tension is iteratively repeated in step S3 until the strain configuration is reached, at which the calculated Tension of the applied intraocular pressure is compensated. If the deformation state or the expansion configuration for the compensation of the intraocular pressure is found for each element, a calculated equilibrium of stresses in the elements, which result from the deformation and expansion, and the intraocular pressure, ie a solution of the finite element model.

In step S4, based on the generated and equilibrium intraocular pressure finite element model, processor 1 0 graphically displays on the display 1 2 a three-dimensional model of the cornea 34. The graph of the cornea model may be displayed by a user of the corneal model Device 1 preferably via input of user commands (eg via mouse, keyboard and / or touch screen) are changed, for example, as in a CAD system in terms of orientation by free rotation in space and / or size or resolution by a zoom function.

In step S5, the processor accepts 1 0 cutting data, for example, according to user commands from a user of the device 1 and / or from a selected file with stored cutting data. The user commands for defining cuts or corresponding cutting data can be entered by the user, for example by means of a computer mouse, a keyboard and / or via a touchscreen in the model shown. The cutting data defines the three-dimensional geometry, dimensions and position of one or more cuts in the cornea 34 and / or in areas of the cornea 34 through the transition 36 into the adjacent sclera 35. The incisions may also be positioned within the ocular tissue be, with or without transection of the front / outer surface 30 of the cornea 35 and the transition surface

the transition 36 and the front / outer surface 350 of the sclera 35. In step S6, the cutting data from the processor 10 is applied to the finite element model of the cornea 34 and the transition 36. That is, the processor 10 determines the elements in the model affected by the cutting data, which are separated from each other by a cut made according to the cutting data.

In step S3, the processor 10 again carries out the solution calculation of the finite element model, as described above, for the finite element model modified by the cutting data. In step S4, the processor 10 generates on the display 1 2 a graphical representation of the section-modified cornea model based on the altered and again with the intraocular pressure in equilibrium finite element model.

The finite element model thus makes it possible to model the cornea 34 and to simulate tissue sections in the cornea 35. The degree of iteration of the steps S3 -> S4 -> S5 -> S6 -> S3 is the length of cuts per iteration step, for example adjustable by the user.

Finally, it should be noted that although the description has shown the execution of steps in a particular order, it will be understood by those skilled in the art that the order of at least certain steps may be changed without departing from the subject of the invention.

Claims

claims

1 . A computerized apparatus (1) for modeling a cornea (34) for the simulation of tissue sections in the cornea (34), comprising a processor (10) programmed to load patient-specific corneal data, a patient-specific corneal finite element model (34 ), and in the finite element model to determine, based on the cutting data defining cutting data, elements separated by the tissue sections, the processor (10) being further programmed to have a first group of tissue fibers parallel to the outer one Surface (30) of the cornea (34) extending main fibers (31) to distribute according to a first distribution function in the finite element model, and a second group of tissue fibers, with inclined, not parallel to the outer surface (30) of the cornea (34) extending Crosslink fibers (32), according to a second distribution function in the finite element model to distribute, where d ie the second distribution function, the cross-link fibers (32) with a non-uniform, decreasing depth distribution function) across the depth (s) of the cornea (34), from the

outer surface (30) of the cornea (34) to the inner surface (33) of the cornea (34) distributed.

2. Device (1) according to claim 1, characterized in that the processor (1 0) is programmed, the cross-link fibers (32) having a sinusoidal course having depth distribution function) over the depth (s) of

To distribute the cornea (34).

Device (1) according to one of claims 1 or 2, characterized in that the processor (10) is programmed to introduce in the finite element model permeability values for fluid exchange in the corneal tissue, which depends on the depth (s) of the cornea (34 ) are dependent.

4. Device (1) according to one of claims 2 or 3, characterized in that the processor (1 0) is programmed to introduce in the finite element model permeability values for fluid exchange in the corneal tissue, which of the depth distribution function

are dependent, with the cross-link fibers (32) over the depth (s) of the cornea (34) are distributed.

5. Device (1) according to one of claims 1 to 4, characterized in that the processor (1 0) is programmed, a transition (36) from the patient-specific finite element model of the cornea (34) on a population-based Scleramodell (35) and the cross-link fibers (32) in the transition (36) with a decreasing depth distribution function

over the depth (t) of the transition (36), from an outer transition surface

which extends from the outer surface (30) of the cornea (34) to the outer surface (350) of the sclera (35), to an inner transitional surface

which extends from the inner surface (33) of the cornea (34) to the inner surface (351) of the sclera (35).

6. Device (1) according to one of claims 1 to 5, characterized in that the processor (1 0) is programmed, the cross-link fibers (32) in the finite element model on several parallel to the outer surface of the cornea (34) extending Layers distribute, and the cross-link fibers (32) in the layers each with a two-dimensional distribution function

to distribute.

7. Device (1) according to one of claims 1 to 6, characterized in that the processor (1 0) is programmed to store different material properties in the finite element model for the first group of tissue fibers and the second group of tissue fibers.

8. Device (1) according to one of claims 1 to 7, characterized in that the processor (1 0) is programmed, the main fibers (31) in the finite element model uniformly on several parallel to the outer surface (30) of the cornea (34 ) and distributed on the surfaces each with a two-dimensional distribution function.

A computer-implemented method for modeling a cornea (34) for the simulation of tissue sections in the cornea (34), which method comprises executing the following steps by a processor (10):

Loading (S 1) patient-specific corneal data,

Generating (S2) a patient-specific finite element model of the cornea (34),

Distributing (S22) in the finite element model of a first group of tissue fibers, with main fibers (31) parallel to the outer surface (30) of the cornea (34), according to a first distribution function, and distributing (S23) in the finite element model of a second group fabric fibers having incline cross-linked fibers (32) not inclining parallel to the outer surface (30) of the cornea (34) according to a second distribution function, wherein the second distribution function does not include the crosslink fibers (32) uniform, decreasing depth distribution function) across the depth (s) of the

Cornea (34), from the outer surface (30) of the cornea (34) to the inner surface (33) of the cornea (34), distributed, and

Determining (S6), based on the tissue sections defining cutting data, of elements in the finite element model that are separated by the tissue sections.

1 0. A method according to claim 9, characterized by distributing (S23) of the cross-link fibers (32) by the processor (1 0) with a sinusoidal course having depth distribution function over the depth (s) of the cornea

(34).

1 1. Method according to one of claims 9 or 10, characterized by introducing (S24) into the finite element model by the processor (10) permeability values for fluid exchange in the corneal tissue, which depend on the depth (s) of the cornea (34). 1 2. The method according to any one of claims 1 0 or 1 1, characterized by introducing (S24) into the finite element model by the processor (1 0) of permeability values for fluid exchange in the corneal tissue, which are dependent on the depth distribution function with which the cross-link fibers

(32) are distributed over the depth (s) of the cornea (34). 1 3. The method according to any one of claims 9 to 1 2, characterized by generating (S21) by the processor (1 0) of a transition (36) from the patient-specific finite element model of the cornea (34) on a population-based Sclera model (35), and distributed by the processor (1 0) of the cross-link fibers (32) in the transition (36) with a decreasing depth distribution function

about the depth (t) of the transition (36), from an outer transition surface

which extends from the outer surface (30) of the cornea (34) to the outer surface (350) of the sclera (35), to an inner one

Transition surface

1 4. A method according to any one of claims 9 to 1 3, characterized by distributing (S23) by the processor (1 0) of the cross-link fibers (32) in the finite element model on several parallel to the outer surface of the cornea (34) extending layers , and by distributing (S23) by the processor (10) the cross-link fibers (32) in the layers each having a two-dimensional distribution function.

A computer program product comprising a non-transient computer readable medium having stored thereon computer program code arranged to control a processor (10) such that the processor (10) carries out the method of any of claims 9 to 14.